Mater Lectionis

In the spelling of Hebrew and some other Semitic languages, matres lectionis (Latin "mothers of reading", singular form: mater lectionis, Hebrew: אֵם קְרִיאָה mother of reading), refers to the use of certain consonants to indicate a vowel. The letters that do this in Hebrew are א aleph, ה he, ו waw (or vav) and י yod (or yud). The yod and waw in particular are more often vowels than they are consonants. In Arabic, the matres lectionis (though they are much less often referred to thus) are alif ا, waw و, and ya' ي.